In the high pressure forming of tubular workpieces by expanding same against a surrounding die or tool, it is common practice to close the ends of the tubular workpiece with plugs, plungers or rams and to introduce a hydraulic medium or some other fluid under elevated pressure into the workpiece to expand the latter outwardly against the surrounding die or tool.
In this high pressure forming method, a mandrel or inner die member is avoided.
If it is desired to provide an opening or cut out in such a hollow body, i.e. in the wall thereof, this has been done hitherto in a separate process outside the internal high pressure shaping apparatus, for example, by plasma or laser cutting or sawing. For this additional step, the shaped workpiece must be removed from the die, transported to another apparatus and clamped or positioned therein to allow cut out of the opening. A simple and rapid stamping with a punch or the like is not possible because of the danger that this will bend the wall at least in a region adjacent the cut out.
In DE 40 35 625, however, a process has been described for producing an opening in a wall expanded against a tool or die in the manner described above. In this case, a recess is provided in the die, the edge of which represents a cutting edge and a plunger supports the portion of the wall disposed within the recess.
In this process, the pressure causes the wall to bulge into the recess. While the wall is supported around the cutting edge of the recess, the deformation of the wall portion inwardly of the cutting edge cannot be fully controlled and some deformation of the wall may occur. A similar process is described in DE-AS 1 552 122 wherein the plunger in the recess recedes at a controlled rate as the workpiece portion is cut out. Here to a fully reliable severing of the cut out piece in a uniform manner cannot be insured.